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In the case of uncertainty, expectation is what is considered the most likely to happen. An expectation, which is a belief that is centred on the future, may or may not be realistic. A less advantageous result gives rise to the emotion of disappointment. If something happens that is not at all expected it is a surprise.

Particularly in social sciences including game theory, expectation plays one of the central roles. In game theory, a Nash equilibrium constitutes a correct and stable set of expectations held by the players. Various other solution concepts of games such as rationalizability have been proposed according to how much knowledge players have on the expectation of other players' actions.